Highly ordered nanoporous films that provide accessibility to an underlying substrate are a key cornerstone of nanofabrication. Bottom-up fabrication technologies based on both anodic oxidation of aluminum and orienting assembled block copolymers have advanced rapidly and are now widely used to generate films with controlled pore sizes below 50 nm that directly access the substrate. However, for pores in the 1-10 nm range, similar milestones have not been reached, and there are no bottom-up technologies that provide well-defined periodic access to a substrate at this length scale without also yielding cracks or access through larger openings. 1-10 nm is an important size range though since the surface area increases dramatically as pore size decreases (at constant void fraction) and many quantum size effects are only observed when the length scale is less than the thermal de Broglie wavelength (which is typically less than 10 nm). As a result developing nanoporous films with smaller pores that access the substrate are important for the development of high sensitivity sensors, high surface area electrodes for fuel cells or photoelectrochemical devices, and nanostructured thermoelectrics or photovoltaics.
Nanofabrication by electrochemical deposition in an ordered porous template can be used to generate new materials for the devices above. However, this technique requires that solution phase species are able to access the substrate and transfer electrons. One way to generate this access is to self-assemble a 3D nanostructure based on a low interfacial curvature phase. One such nanostructure is the phase based on the gyroid minimum surface. This zero mean curvature surface divides space into two continuous, non-intersecting domains. When a wall replaces the gyroid surface, a tricontinuous structure results (one wall and two pore systems). Tricontinuous gyroid structures are actually quite common in block copolymer systems and typically occur between the lamellar and cylindrical phases on the spectrum of interfacial curvature. (It should be noted that there may some microporosity in the wall that connects the two pore systems. Regardless of this, the films are still referred to as “tricontinuous”). However, the synthesis of nanoporous gyroid structures in thin film morphology with small pore sizes has proven very challenging.